Effect of the antimicrobial peptide Scy-hepc on the motility of intestinal commensal bacteria contributing to the growth and immunity promotion in Epinephelus akaara

Emerging evidence strongly supports that the beneficial effects of probiotics and antimicrobial peptides (AMPs) on the host can be ascribed to modifications in gut microbial colonization, leading to the optimization of the host intestinal ecosystem. Our previous study found that long-term (one-year) daily administration of the AMP Scy-hepc significantly enhanced the growth of mariculture fish. However, the impact of Scy-hepc feeding on the colonization of gut microbiota and its potential contributions to host growth and immunity remains unclear. This study aimed to investigate the mechanism of the intestinal absorption and actions on gut microbiota in Epinephelus akaara following Scy-hepc feeding. 16S rRNA sequencing showed that 35 days of Scy-hpec feeding significantly promoted the growth of E. akaara compared to probiotics, antibiotics and vector group, that was attributed to alterations in the microbiota colonization in the foregut and midgut, characterized by increased abundance of probiotics (Rhizobiaceae and Lysobacter), and decreased abundance of opportunistic pathogens (Psychrobacter and Brevundimonas). Furthermore, similar to the effect of antibiotics feeding, Scy-hepc feeding significantly improved host survival rate (73.75%, p < 0.05) during Edwardsiella tarda infection. We further demonstrated that Scy-hepc could be absorbed by the fish foregut (20-40 min) and midgut (20-30 min) using western blot, Elisa and immunofluorescence. Subsequently, it was discovered that the absorption of Scy-hepc has an impact on the motility and colonization of commensal bacteria by regulating the assembly of bacterial flagella. Both probiotics Bacillus thuringiensis and opportunistic pathogens Vibrio harveyi, which were isolated from E. akaara intestine, were affected in terms of their motility genes (PomA and PomB/MotA and MotB) by Scy-hepc.